Generally when a well is drilled at least one hydrocarbon bearing formation is intersected. Part of the process of completing the well includes installing a liner within the well where the liner also intersects the hydrocarbon bearing formation. Once the liner is in place ports are opened up through the liner so that fluids, usually at least water and oil, may flow from the hydrocarbon bearing formation to the interior of the liner. In a newly completed well, in many instances, there is sufficient pressure within the hydrocarbon bearing formation to force the fluid from the hydrocarbon bearing formation to the surface. After some period of time the pressure gradient drops to the point where the fluids from a hydrocarbon bearing formation are no longer able to reach the surface.
Once the fluids are no longer able to naturally reach the surface artificial lift may be employed. One form of artificial lift is known as gas lift. Gas lift involves, at various downhole points in the well, injecting gas into the central passageway of the production tubing string to lift the well fluid in the string. The injected gas, which is lighter than the well fluid displaces some amount of well fluid in the string. The displacement of the well fluid with the lighter gas reduces the hydrostatic pressure inside the production tubing string and allows the reservoir fluid to enter the wellbore at a higher flow rate.
In a conventional gas lift operation a production tubular is assembled on the surface and includes a packer and a number of gas lift mandrels. Each mandrel has a check valve and a conventional injection pressure operated gas lift valve.
The production tubular is then run into the well so that the packer may be set at some point above the ports in the liner that provide access to the hydrocarbon bearing formation. Once the packer is set fluid may flow from a hydrocarbon bearing formation into an annular area between the liner and the production tubular. The packer prevents the fluid from flowing into the annular area above the packer however the fluid may flow to the bottom of the production tubular and into the production tubular. Once the fluid is in the production tubular it may flow upwards to a level dependent upon the hydrocarbon bearing formation pressure gradient. The fluid in the production tubular will generally flow up past the annular packer and will flow upwards past at least one of the side pocket mandrels. Each check valve in the side pocket mandrels prevents the fluid within the production tubular from flowing through the side pocket mandrel and into the annular area above the packer.
In order to begin producing the fluid to the surface, high-pressure gas such as nitrogen is injected into the annular area between the liner and the production tubular. The only outlet for the high-pressure gas is through the gas lift valves into the gas lift mandrels and then into the interior of the production tubular. As the high-pressure gas reaches the gas lift valve the high-pressure gas flows into the gas lift valve through ports in the side of the gas lift valve. The ports are located between the gas lift valve seat and the bellows. The high-pressure gas acts on the bellows adapter and the bellows compressing the bellows which in turn lifts the ball off of the seat. With the ball off of the seat the high-pressure gas is able to flow through the seat into the check valve. The high-pressure gas then acts upon the check valve, where the check valve has a check dart that the high pressure gas compresses against a spring lifting the check dart off of a check pad allowing the high-pressure gas to flow through the check valve and into the gas lift mandrel. As the gas flows out of the gas lift mandrel and into the interior of the production tubular adjacent the gas lift mandrel the high-pressure gas causes the fluid to become a froth. The effect is similar to blowing bubbles into milk through a straw. The column of fluid which is now froth has a much lower density and therefore a lower head pressure than a pure liquid column. The natural formation pressure in conjunction with the flow of high pressure gas now flowing upward through the production tubular lifts the froth, and thus the hydrocarbons and other fluid, to the surface.